Experimental and numerical investigation on the cold harvest of composite phase change materials for building energy conservation

This paper investigates the cold energy storage of a horizontal shell-tube latent heat thermal energy storage (LHTES) unit for the cold harvest during night time. An experimental apparatus containing a horizontal circular tube with circumferential heating/cooling was designed and developed. Paraffin based phase change material (PCM) with a melting temperature of 27 degrees C was adopted as the cold harvest media. To improve the heat transfer rate, multi-walled carbon nanotubes (MWCNTs) were mixed with the paraffin to form a composite PCM with high thermal conductivity. A corresponding model of the composite PCM was developed and verified against the experimental data. Numerical simulations were performed for different boundary temperatures and concentrations of MWCNTs. The results show that when the heat transfer temperature difference is 20 degrees C, 0.05 wt% nanoparticles increase the melting rate of PCMs. When the heat transfer temperature difference was 40 degrees C, 0.10 wt% nanoparticles significantly affect the PCM melting rate. For low or high temperature (heat transfer temperature difference of 10 degrees C and 80 degrees C), the addition of nanoparticles is not conducive to improving the melting rate.